Bhasin S, et al. - As a part of this study clarification was yielded with regard to the participant-level factors that contributed to inter-individual variability in testosterone levels during testosterone therapy. It also ascertained if polymorphisms in genes encoding testosterone-metabolizing enzymes elucidated the change in the on-treatment testosterone concentrations in men who were randomized to testosterone arm in TOM Trial. The baseline participant characteristics were responsible for only a minor proportion of the variance in on-treatment testosterone levels. Multiple dose titrations were warranted for the maintenance of on-treatment testosterone levels in the target range. An advanced research was needed for exploring the role of SHBG and AKR3C1 polymorphisms as contributors to variations in on-treatment testosterone levels.